When processing precision machine parts, optical machine parts and the like, various kinds of working oil such as cutting oil, pressing oil, drawing oil, hot-treating oil, rust preventing oil, lubricating oil and the like, grease, wax and the like are used. It is necessary to remove contamination caused by them at the final stage, and the removal has been generally carried out using a solvent.
As a joining process for electronic circuitry, soldering has been the most generally carried out. It is usual that a metal surface to be soldered is previously treated with flux containing rosin as a main component for the purpose of removing any oxide on the surface to be soldered, cleaning said surface, preventing re-oxidation thereof and improving the solder-wetting property. As a soldering process, there are processes such as a process comprising dipping a substrate in flux of a solution state, thereby attaching the flux on the substrate surface, and thereafter supplying a melted solder thereto; and a process comprising supplying a paste obtained by mixing powders of flux and solder to a spot to be soldered, followed by heating. In any case, after soldering, it is necessary to sufficiently remove the flux residue, which causes metal corrosion and deterioration of insulation.
In carrying out cleaning and removal thereof, a solvent such as 1,1,2-trichloro-1,2,2-trifluoroethane (hereinafter referred to as CFC113) and a mixture of CFC113 and an alcohol has been used from a viewpoint of many characteristic features such as non-flammability, low toxicity and superior dissolution property. However, there had been noted an environmental pollution problem of the earth, including ozonosphere destruction, due to CFC113, and in Japan, the production thereof had been wholly abolished in the end of 1995. As a substitute for CFC113, there have been proposed hydro-chloro-fluorocarbons such as a mixture of 3,3-dichloro-1,1,1,2,2-pentafluoropropane and 1,3-dichloro-1,1,2,2,3-pentafluoropropane (hereinafter referred to as HCFC225) and 1,1-dichloro-1-fluoroethane (hereinafter referred to as HCFC141b). However, in Japan, it is intended to inhibit the use thereof by 2020 because of a little ozonosphere destruction ability.
Further in recent years, there have been proposed non-flammable fluorine solvents, such as hydro-fluorocarbons (hereinafter referred to as HFC), hydro-fluoroethers (hereinafter referred to as HFE) and the like, which are completely free from ability to cause ozonosphere destruction, and which are completely free of chlorine atoms. However, these solvents are inferior in dissolution ability because of the absence of chlorine atoms, so that these solvents by themselves cannot be used as a cleaning agent. Accordingly, JP-A 10-36894 and JP-A 10-192797 disclose a technique, according to which cleaning is carried out with a cleaning agent obtained by adding a high boiling solvent to HFC or HFE, and thereafter HFC or HFE is used as a rinsing agent.
However, since both inventions propose use of a high boiling solvent for the cleaning agent, there remain problems such that the drying property of a material to be cleaned decreases and soil accumulating in the cleaning agent increase, thereby causing re-adhesion of soil on the surface of a material to be cleaned. Therefore, in order to improve such cleaning methods, JP-A 2000-8096 proposes a process, according to which there is provided a rinsing tank in which HFC or HFE having low soil dissolution ability and superior drying property are placed, so that the high boiling component having superior dissolution property is rinsed, and at the same time, a rinsing liquid in the rinsing tank is used to separate soil accumulating in the cleaning agent. However, the rinsing liquid in the rinsing tank is used, and therefore, the soil-separating ability remarkably deteriorates, so that the soil cannot be separated with high efficiency.
As described above, in the existing circumstances, the cleaning agent and the cleaning method so far proposed as a substitute of CFC113 have many problems when used as a cleaning agent such that even if used for cleaning, some will be prohibited to be used in the future because of the problem of ozonosphere destruction, or even if soil accumulating in the cleaning agent can be separated in a continuous manner, the separating efficiency of soil in the cleaning agent remarkably deteriorates, because the rinsing liquid in the rinsing tank is used up.